Methods of inhibiting corrosion using halo-benzotriazoles

ABSTRACT

A method of preparing halo-benzotriazoles is disclosed. The method involves mixing an aqueous solution of sodium hypohalite with an aqueous slurry or suspension of a benzotriazole. Preferred sodium hypohalites are sodium hypochlorite or sodium hypobromite and the preferred benzotriazole is tolyltriazole.

This application is a continuation-in-part of application Ser. No.08/778,705 filed Jan. 3, 1997, which is a continuation-in-part ofapplication Ser. No. 08/407,173 filed Mar. 21, 1995, now abandoned.

FIELD OF THE INVENTION

The present invention relates to the control of corrosion in aqueoussystems. More particularly, the present invention relates to theinhibition of corrosion of steel and copper alloys in aqueous systemsthrough application of halo-benzotriazoles to the aqueous system.

BACKGROUND OF THE INVENTION

The use of triazoles for inhibiting the corrosion of copper and ironalloys in a wide variety of aqueous and non-aqueous systems is wellknown. In industrial cooling water systems, benzotriazole andtolyltriazole are used most often. Tolyltriazole is generally preferredbecause of its lower cost. Triazoles are film forming materials thatprovide efficient coverage of metal or metal oxide surfaces in a systemthereby providing protection against corrosive elements present in anaqueous system. In addition to the film forming tendency of variousazoles, they also precipitate soluble, divalent copper ions. Theprecipitation prevents transport of copper ions to ferrous surfaces,where galvanic reactions between copper ions and iron atoms leads topitting corrosion of the ferrous metal.

While the use of azoles for corrosion inhibition is widespread, thereare drawbacks to their use, specifically with tolyltriazole. The mostimportant drawbacks are experienced when azoles are used in combinationwith oxidizing halogens. Oxidizing halogens such as elemental chlorine,bromine, their hypohalous acids, or their alkaline solutions (i.e.,solutions of hypochlorite or hypobromite ion) are the most commonmaterials used to control microbiological growth in cooling watersystems. When copper or iron alloys that have previously been protectedwith azoles are exposed to an oxidizing halogen, corrosion protectionbreaks down. After breakdown, it is difficult to form new protectivefilms in tolyltriazole treated cooling systems that are beingchlorinated, particularly continuously chlorinated. Very high dosages oftolyltriazole are frequently applied in an attempt to improveperformance, often with limited success.

The degradation of protection of azole films in the presence ofoxidizing halogens is well-documented in the literature. For example, R.Holm, et al., concluded that hypochlorite penetrates an intact triazolefilm, leading to higher corrosion rates, and that secondly, hypochloriteattacks the prefilmed triazole surface, disrupting or degrading the film(53rd Annual Meeting of the International Water Conference, Paper No.IWC-92-40, 1992). Lu, et al., also studied interactions of triazolefilms with hypochlorite on copper and copper alloy surfaces ("Effects ofHalogenation on Yellow Metal Corrosion: Inhibition by Triazoles",Corrosion, 50, 422 (1994)). Lu, et al., concluded:

(a) prefilmed tolyltriazole on copper and brass surfaces undergoesdecomposition during chlorination;

(b) the stability of prefilmed tolyltriazole on copper and brass toNaOCl was improved when tolyltriazole was added to the hypochloritesolution;

(c) clean (i.e., non-prefilmed) copper surfaces did not develop goodprotective films when placed in solutions containing mixtures oftolyltriazole and NaOCl.

Thus, the combination of tolyltriazole with NaOCl did not produce acomposition capable of efficient film formation and corrosioninhibition.

The nature of the reaction products when azoles are exposed to oxidizinghalogens in a cooling water system is not clear. The literature teachesthat a compound is formed when chlorine and tolyltriazole are combinedin cooling waters, and that it responds to analytical tests forchlorine. For example, Vanderpool, et al., state that chlorine reactsreversibly with tolyltriazole to produce N-chloro-tolyltriazole. Theyspecifically state, "presumably this compound is not itself aninhibitor." Rather, they teach that it is readily hydrolyzed to theoriginal tolyltriazole and hypochlorous acid so that free tolyltriazolebecomes available for corrosion inhibition ("Improving the CorrosionInhibitor Efficiency of Tolyltriazole in the Presence of Chlorine andBromine", NACE Corrosion/87, Paper No. 157 (1987)). Hollander and Maystated they were able to isolate 1-chloro-tolyltriazole from stored,more highly concentrated solutions, but they also teach that "at lowconcentrations (less than 10 mg/L) rapid hydrolysis made it impossibleto isolate the chloro adducts." Based upon proton NMR analysis, thematerial Hollander and May isolated was chloro-tolyltriazole.

Another observation is that a very characteristic odor is presentwhenever tolyltriazole and chlorine are combined in cooling waters.

In contrast, the present authors have shown that chloro-tolyltriazoledoes not respond to analytical tests for chlorine, despite extendedboiling. And solutions of chloro-tolyltriazole, surprisingly, do notproduce the characteristic odor. Thus chloro-tolyltriazole is clearlydifferent from the tolyltriazole-chlorine reaction product that forms insitu in cooling water systems.

There are also references in the literature to 5-chlorobenzotriazole(i.e., CAS number 94-97-3!). In "The Water Drop", Volume I No. 2, 1985,Puckorius & Associates state that chlorinated tolyltriazole is effectiveas a corrosion inhibitor and cite R.P. Carr as a reference. A literaturereview of published work by Carr indicates that he actually teaches thatreactions between tolyltriazole and chlorine do not occur under coolingwater conditions ("The Performance of Tolyltriazole in the Presence ofSodium Hypochlorite Under Simulated Field Conditions", NACE Corrosion/83Paper No. 283, 1983). In this Corrosion/83 paper, Carr does discuss theinhibiting action of a chloro-azole but it is a reference to earlierliterature and specifically to the action of 5-chlorobenzotriazole andrelated aryl substituted azoles in sulfuric acid solutions ("Effects ofSubstituted Benzotriazole on the Electrochemical Behavior of Copper inH₂ SO₄ ", Wu et al., Corrosion, Volume 37, No. 4,223 (1981)). Since the1985 Puckorius reference, there has been widespread use of tolyltriazolein chlorinated cooling systems with well established performancedifficulties, indicating a continuing, unsolved problem in the art.

Other problems are well-known when tolyltriazole and oxidizing halogensare combined in cooling waters. These include a loss in the extent ofprecipitation of transition metal ions such as copper, thus leading toimproved transport and galvanic corrosion, a change in the response ofthe standard spectrophotometric test for tolyltriazole, leading tounintentional overfeed, and the objectionable odor mentioned above. Thisodor can be sensed even when the cooling water originally contained 1ppm tolyltriazole, or less. Since cooling water often passes overcooling towers, evaporation and drift release the objectionable odor tothe local environment.

The present inventors believe that the odorous material isN-chloro-tolyltriazole, that it forms reversibly with tolyltriazole indilute solution, and that it is absent in the final product when thereaction is run in concentrated solution, i.e., tolyltriazole+OCl⁻→N-chloro-tolyltriazole-(intermediate)→chloro-tolyltriazole. The presentinventors have found no evidence of reversion of chloro-tolyltriazole toeither the odorous intermediate or to tolyltriazole. Nor is there anyevidence of reactions between hypochlorite and chloro-tolyltriazole indilute aqueous solutions.

SUMMARY OF THE INVENTION

The present inventors have discovered that halo-benzotriazoles such aschloro-tolyltriazole and bromo-tolyltriazole are more effective thantolyltriazole in inhibiting corrosion in aqueous systems. Thehalo-benzotriazoles are substantially more effective than tolyltriazolein the presence of chlorine. Furthermore, when chloro-tolyltriazole isexposed to chlorine, an objectionable odor does not form and thequantity of chlorine that is required to produce a residual in theaqueous system is reduced. A process for preparation of aqueoussolutions of halo-benzotriazoles is also disclosed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present inventors have discovered that halo-benzotriazoles such aschloro-tolyltriazole and bromo-tolyltriazole are more effective thantolyltriazole in inhibiting corrosion in aqueous systems. Thehalo-benzotriazoles are substantially more effective corrosioninhibitors than tolyltriazole in the presence of chlorine. The efficacyof the present invention is surprising given the prior knowledge thatchlorination of an azole treated system leads to degradation ofcorrosion inhibition performance. Furthermore, the halo-benzotriazolesof the present invention are not subject to the formation ofobjectionable odors when exposed to chlorine as is tolyltriazole, thequantity of chlorine that is required to produce a residual in theaqueous system is notably reduced in comparison to systems treated withtolyltriazole, and the treatment is effective in the presence of sulfideions.

It was discovered that the ex situ preparation of a halo-benzotriazoleprovided a corrosion inhibitor which exhibited a surprising andunexpected activity when compared to a treatment comprising a mixture ofa benzotriazole and a halogen. The results of the studies of the presentinvention clearly show that mere mixtures of a benzotriazole and ahalogen in a cooling water system do not provide the corrosioninhibiting effect of the addition of a halo-benzotriazole prepared exsitu. As further evidence of the surprising activity of an ex situprepared halo-benzotriazole, the present inventors found that thechlorine demand of a system treated in accordance with the presentinvention was significantly reduced. Furthermore, in systems treated inaccordance with the present invention the objectionable odor common tosystems treated with a triazole and halogen was absent.

The halo-benzotriazoles of the present invention can include chloro-,fluoro-, bromo- and iodo- as well as haloalkyl (trifluoromethyl)benzotriazoles. Preferred are chloro-tolyltriazole andbromo-tolyltriazole. The azole may include tolyltriazole, benzotriazole,butylbenzotriazole, mercaptobenzothiazole and the like. The preferredazole is tolyltriazole.

The preferred benzotriazole, tolyltriazole, is such that the preferredhalo-benzotriazole is chloro-tolyltriazole or bromo-tolyltriazole. Thepreparation of the preferred chloro-tolyltriazole can be by any suitablemeans. Examples of preparation methods include but are not limited toreactions with hypochlorite, N-chlorosuccinimide, and other chlorinatingagents. A method of forming chloro-tolyltriazole is through the reactionof tolyltriazole with hypochlorite, in which case the final reactionmixture is an alkaline solution that can be used with or without furthermodification. Alternatively, chloro-tolyltriazole can be formed throughthe reaction of tolyltriazole with hypochlorite in acetic acidsolutions, (i.e., hypochlorous acid) and then isolated as a solid. Forconvenience of application, the solid can be redissolved in alcoholssuch as methanol or 2-propanol, aqueous solutions of alcohols or strongalkaline solutions such as sodium hydroxide or potassium hydroxide.

The preparation of bromo-tolyltriazole can be by any suitable means.Examples of preparation methods include but are not limited to reactionswith hypobromite, bromine, and other brominating agents. A method offorming bromo-tolyltriazole is through the reaction of tolyltriazolewith bromine in an aqueous solution and then isolating it as a solid.For convenience of application, the solid can be dissolved in a strongalkaline solution such as sodium hydroxide or potassium hydroxide.

In treating an aqueous system in accordance with the present invention,the chloro-tolyltriazole (hereinafter Cl-TTA) is preferably fedcontinuously to the water. A preferred treatment concentration rangesfrom about 0.5 to 10 parts per million, most preferably at about 3 partsper million. Continuous feed is not, however, a requirement. Thechloro-tolyltriazole can be fed at a concentration sufficient to form aprotective film and thereafter feed can be discontinued for extendedperiods of time.

The halo-benzotriazole treatment of the present invention can be used incombination with other corrosion and/or deposit inhibiting treatmentsknown in the art including but not limited to phosphates, phosphonates,acrylic homo- and copolymers, chelants, and oximes.

The present inventors have discovered a process for producing a high pHaqueous solution of halo-benzotriazole, the process comprises adding asodium hypochlorite solution to a slurry of4(5)-methylbenzotriazole/tolyltriazole (TTA) in water at 47°-50° C. Theresulting reaction produces a high pH solution containing Cl-TTA as itsmajor component. This new process eliminates the use of acetic acid andthe need to isolate solid Cl-TTA. The resulting aqueous solution iseasily transported, handled and applied as a corrosion inhibitor inaqueous systems. While the reaction of sodium hypochlorite with aqueoussolutions of the sodium salt of TTA also resulted in the formation of anaqueous solution of Cl-TTA, the yield was lower so this reaction is lessdesirable.

In one example of the preferred method of preparation of Cl-TTA, anaqueous slurry of TTA was reacted with sodium hypochlorite in a 1:1molar ratio. The temperature was 47°-50° C. and the pH ranged from 8-9to about 12 at the end of the reaction. The resulting mixture contained1.2-1.4 wt. % residual TTA. During the initial stages the reactionmixture is a slurry, but as the pH increases over 10, a solution forms.

Examples 13 and 14 below relate to the new method of preparation ofCl-TTA and Br-TTA while comparative Example 15 relates to the adaptationof the prior "acetic acid" method of preparing Cl-BZT to the preparationof Cl-TTA. These examples show that the new method of this inventionresults in a higher yield without the need to handle acetic acid orsolid product.

The present invention will now be further described with reference to anumber of specific examples which are to be regarded solely asillustrative and not as restricting the scope of the present invention.

EXAMPLES Example 1

The preparation of the solid samples was as follows:

Tolyltriazole (hereinafter TTA) (30 g, 0.225 mol) was dissolved inaqueous acetic acid (60 mL, 1:1 ratio) by heating to 32° C. Sodiumhypochlorite (366 g, 5.25% sodium hypochlorite as a bleach solution) wasadded while maintaining the reaction temperature at ˜20° C. Followingthe addition, the reaction mixture was stirred at room temperature for24 hours. A sticky precipitate formed during this time. The solid wasfiltered and taken into methylene chloride. The solid that did notdissolve was filtered and identified as a mixture of Cl-TTA with minoramounts of TTA and dichloro-tolyltriazole (di-Cl-TTA). The methylenechloride was removed to obtain a yellow solid which was identified as amixture of Cl-TTA with minor amounts of di-Cl-TTA. Unless noted, thislatter solid was used in the following Examples.

Example 2

A slurry of TTA (50 g, 0.376 mol) in 25 g of water was warmed to 35° C.Sodium hypochlorite (27.9 g, 0.376 mol, added as 226.8 g of a 12.3%sodium hypochlorite solution) was added over a period of 2 hours. Afterthe addition, the reaction was kept at 45° C. for one hour. During theaddition the pH of the reaction mixture increased to 12 and the solidsdissolved. The final product was analyzed by ¹ H and ¹³ C NMR and LC-UVand found to be composed of 81.9% Cl-TTA, 8.8% residual TTA, and 9.3%di-Cl-TTA based on the relative areas in the UV spectra.

On dilution to 1 to 100 ppm azole, with or without pH adjustment toabout 7.2, there was no odor from the halo-benzotriazole solution of thepresent invention.

Example 3

In the schemes below, TTA was present at 100 ppm, in contrast to Example2 where the initial slurry contained about 200,000 ppm. "x" denotes astoichiometric ratio. ##STR1##

Example 4

Cl-TTA, prepared as a solid according to Example 1, was dissolved inmethanol and charged to a simulated cooling water solution. The solutioncontained 319 ppm Ca (calculated as CaCO₃), 7 ppm Mg (calculated asCaCO₃), 190 ppm NaHCO₃, 882 ppm Na₂ SO₄, 1184 ppm NaCl, 5 ppm Cl-TTA,and 2.4 ppm of hydroxyethylidene diphosphonic acid (HEDP). Hypochloritewas absent. The solution was maintained at 120° F. by an admiralty brassheater tube and at pH=7.2 to 7.5 by a pH controller equipped to feedsulfuric acid on demand. The solution was recirculated past the heaterand past both admiralty and copper/nickel alloy corrosion rate meters(CRM). After 1 hour the solution was drained and replaced by anidentical solution with no Cl-TTA. This solution was fed to overflowwhich replenished the system with fresh solution at a rate of about 4%by volume per hour. This system was maintained under these conditionscontinuously until the bright admiralty tube was tarnished, at whichpoint the experiment was terminated. Comparisons were made to identicalexperiments with TTA and benzotriazole.

                  TABLE I                                                         ______________________________________                                        Admiralty Tube Appearance                                                     Pretreatment                                                                             40 hours     94 hours 336 hours                                    ______________________________________                                        CI-TTA     Bright       Bright   Tarnished                                    TTA        Bright       Tarnished                                                                              *                                            Benzotriazole                                                                            Tarnished    *        *                                            ______________________________________                                    

                  TABLE II                                                        ______________________________________                                               Admiralty     Cu/Ni                                                           Corrosion Rate (mpy)                                                                        Corrosion Rate (mpy)                                     Pretreatment                                                                           40 hrs. 94 hrs. 336 hrs.                                                                            40 hrs.                                                                             94 hrs.                                                                             336 hrs.                           ______________________________________                                        CI-TTA   0.2     0.3     0.5   0.7   0.4   0.8                                TTA      <0.1    2.2     *     N/A   5.2   *                                  Benzotriazole                                                                          1.3     *       *     2.0   *     *                                  ______________________________________                                         *Experiment previously terminated.                                       

Example 5

Corrosion tests were carried out in the apparatus described in Example 4with water containing 500 ppm Ca, 250 ppm Mg, 25 ppm Malk, 15 ppm o-PO₄,3 ppm tetrapotassium pyrophosphate, 10 ppm of a 3:1, low molecularweight, acrylic acid/allyl 2-hydroxypropyl sulfonate ether copolymer,2.4 ppm HEDP, a 3 ppm of either Cl-TTA or TTA. The pH was maintained at7.2 with a blended mixture of air and carbon dioxide at 120° F. for 18hours. Electrochemical corrosion rates were measured using admiraltybrass (ADM) and low carbon steel (LCS) working electrodes. All testsalso had both admiralty and LCS coupons in contact with the solution.The method differed from Example 4 in that the azole was fedcontinuously at 3 ppm during these experiments. The azole was suppliedby dissolving the solid in potassium hydroxide solution and thendiluting it into the feedwater for the system. Each experiment wasduplicated: once with an admiralty brass heated tube, and once with alow carbon steel heated tube. Corrosion rates were measured as inExample 4 from admiralty and LCS working electrodes, and by weightchanges of admiralty and LCS coupons. Rates for the coupons weremeasurer for the initial day of each run, and a "differential" rate wascalculated for the remaining days of the run by offsetting the initialrate from the overall rate.

                  TABLE IlI                                                       ______________________________________                                        CRM Corrosion Rates: Values at end of six days (mpy)                                                ADM                                                             LCS Heated Surface                                                                          Heated Surface                                                  CI-TTA                                                                              TTA         CI-TTA  TTA                                         ______________________________________                                        LCS       0.2     0.4         0.45  0.75                                      ADM       0.00    0.00        0.05  0.07                                      ______________________________________                                    

                  TABLE IV                                                        ______________________________________                                        Gravimetric Coupon Corrosion Rates (mpy)                                      (First day and differential rates)                                                                    ADM                                                               LCS Heated Surface                                                                        Heated Surface                                                    CI-TTA                                                                              TTA       CI-TTA  TTA                                       ______________________________________                                        Day 1 LCS     4.6     3.0       3.4   2.9                                     Day 6 LCS (diff.)                                                                           0.25    0.33      0.25  0.25                                    Day 1 ADM     1.9     2.1       1.6   1.8                                     Day 6 ADM (diff.)                                                                           0.00    0.20      0.00  0.10                                    ______________________________________                                    

Example 6

The method of Example 5 was followed, except a solution of sodiumhypochlorite was added after 20 hours and continued for an additional 72hours. The feed rate of the sodium hypochlorite was controlled toproduce a "chlorine residual" of about 0.1 to 0.3 ppm as Cl₂ using astandard DPD spectrophotometric test on the recirculating water. For theexperiment with Cl-TTA, the feed rate of the sodium hypochlorite wasabout 30% of that required for TTA. For TTA, the characteristic odor wasdetected immediately after the first hypochlorite was added. WithCl-TTA, there was no odor upon initiating hypochlorite addition, andonly a trace was sensed just prior to concluding the four day run.

                  TABLE V                                                         ______________________________________                                        CRM Corrosion Rates: Values at 90 hour mark (mpy)                                          LCS Heated Surface                                                            CI-TTA                                                                              TTA                                                        ______________________________________                                        LCS            0.5     2.3                                                    ADM            0.06    0.02                                                   ______________________________________                                    

                  TABLE VI                                                        ______________________________________                                        Gravimetric Corrosion Rates (mpy)                                                             LCS Heated Surface                                                            CI-TTA                                                                              TTA                                                     ______________________________________                                        Day 2 to 4 LCS    1.1     2.6                                                 Day 4 LCS (diff.) 0.4     1.4                                                 Day 2 to 4 ADM    1.1     1.2                                                 Day 4 ADM (diff.) 0.15    0.85                                                ______________________________________                                    

Example 7

Solutions of azole at 6 ppm were made in deionized water, and the pH wasadjusted to 7.0. Cu⁺² ion was added (0.1 ppm from cupric sulfate) andthe pH was again adjusted to 7.0. A sample was digested with nitricacid, analyzed for copper, and a second sample was filtered (0.2 micronpore size), digested, and analyzed for copper. The ratio was expressedas "% soluble Cu":

                  TABLE VII                                                       ______________________________________                                        Sample        % Soluble Cu                                                    ______________________________________                                        TTA           15                                                              TTA + NaOCl   90                                                              CI-TTA        13                                                              ______________________________________                                    

Example 8

Admiralty brass corrosion coupons and working electrodes were coatedwith a sulfide layer by exposing the metal to a sodium sulfide solutionfor 18 hours. These samples were rinsed and dried. Corrosion tests werecarried out in aqueous solutions in stirred beakers containing 500 ppmCa, 250 ppm Mg, 25 ppm Malk, 15 ppm o-PO₄, 3 ppm tetrapotassiumpyrophosphate, 10 ppm of a 3:1, low molecular weight, acrylic acid/allyl2-hydroxypropyl sulfonate ether copolymer, 2.4 ppm HEDP, and the pH wasmaintained at 7.2 with a blended mixture of air and carbon dioxide at120° F. for 18 hours. Electrochemical corrosion rates were measuredusing admiralty brass or low carbon steel working electrodes. All testsalso had both admiralty and LCS coupons in contact with the solution.

Each solution was tested with and without addition of sodiumhypochlorite (added after 1 hour exposure). In a separate, but otherwiseidentical experiment, clean low carbon steel working electrodes wereused in place of the sulfide-exposed admiralty brass, but thesulfide-exposed brass coupons were present as a source of copper. At theconclusion of the experiment, a sample of the supernatant solution wastaken and analyzed for copper. Analyses were taken with and withoutfiltration through a 0.2 micron membrane filter.

                  TABLE VIII                                                      ______________________________________                                        Admiralty Low Carbon                                                                     Brass   Steel                                                                 Corrosion                                                                             Corrosion                                                         NaOCl Rate      Rate     Copper (ppm)                                  Azole    (ppm)   (mpy)     (mpy)  Unfiltered                                                                           Filtered                             ______________________________________                                        none     0       1.01      5.4    0.354  0.103                                3 ppm TTA                                                                              0       0.07      1.2    0.014  0.014                                3 ppm CI-TTA                                                                           0       0.060, 0.05                                                                             1.0    0.005  0.004                                none     2.0     2.09      5.2    0.417  0.059                                3 ppm TTA                                                                              2.0     0.45      2.6    0.133  0.066                                3 ppm CI-TTA                                                                           2.0     0.13      1.7    0.086  0.039                                ______________________________________                                    

Example 9

A synthetic sea water was formulated from deionized water plus 1010 ppmCa as CaCO₃, 5226 ppm Mg (as CaCO₃), 18971 ppm Cl, 2660 ppm SO₄, 117 ppmM-alkalinity (as CaCO₃), 5 ppm azole (see below), and the pH wasmaintained at 7.8 with a blended mixture of air and carbon dioxide at100° F.

Admiralty brass electrodes were exposed to this medium for 1 hour andthen they were transferred to identical water with no azole present.Electrochemical corrosion rates were measured for 18 hours.

                  TABLE IX                                                        ______________________________________                                                     Mean Electrochemical                                             Azole          Corrosion Rate (mpy)                                           ______________________________________                                        Benzotriazole  40                                                             5-Butylbenzotriazole                                                                         15                                                             Tolyltriazole  6                                                              Chloro-tolyltriazole                                                                         3.2                                                            ______________________________________                                    

Example 10

Sodium hypochlorite (12.2%, 204.9 g, 0.336 mol) was added over 90minutes to a stirring slurry of benzotriazole (40 g, 0.336 mol) in 30 gof water at room temperature. Following the addition, the reactionmixture was held at 45°-50° C. for one hour. Upon cooling, a precipitateformed. A clear yellow solution was obtained after adjusting the pH to11. The final product was analyzed by LC/MS and ¹³ C and ¹ H NMR andfound to be composed of 54.6% chloro-benzotriazole (Cl-BZT), 23.9%residual benzotriazole, and 21.5% di-chloro-benzotriazole (di-Cl-BZT).

Example 11

Bromine (12.5 g, 0.078 mol) was added to a stirring slurry of TTA (10 g,0.075 mol) in 66 g of water in a reactor protected from light, whilemaintaining the temperature at <25° C. After the addition, the reactionmixture was held at 35°-40° C. for one hour. Upon cooling, adjusting thepH to 11-12 did not produce a clear solution. The small amount ofprecipitate that formed upon standing was removed by filtration, the pHof the filtrate was adjusted to neutral, and the resulting precipitatefiltered. This solid was characterized by LC/MS and ¹³ C and ¹ H NMR andfound to be composed of 90.5% bromo-tolyltriazole (Br-TTA), 4.9%residual TTA, and 4.2% di-bromo-TTA.

Example 12

The method of Example 8 was followed, using samples from Examples 2, 11and 12 at 1 to 4 ppm total actives. The following were the 18 houraveraged electrochemical corrosion rates:

                  TABLE X                                                         ______________________________________                                                                          Average                                              Conc.                    Corrosion                                   Azole    (ppm)   Source     NaOCl Rate (mpy)                                  ______________________________________                                        CI-BZT   1       Ex. 11     none  0.21                                                 2                        0.09                                                 4                        0.03                                        CI-BZT   1       Ex. 11     2 ppm 0.55                                                 2                        0.25                                                 4                        0.09                                        CI-TTA   1       Ex. 2      none  0.14                                                 2                        0.09                                                 4                        0.08                                        CI-TTA   1       Ex.2       2 ppm 0.58                                                 2                        0.24                                                 4                        0.09                                        Br-TTA   1       Ex. 12     none  0.17                                                 2                        0.11                                                 4                        0.07                                        Br-TTA   1       Ex. 12     2 ppm 0.45                                                 2                        0.16                                                 4                        0.09                                        TTA      1                  none  0.13                                                 2                        0.14                                                 4                        (n/a)                                       TTA      1                  2 ppm (n/a)                                                2                        0.45                                                 4                        0.27                                        ______________________________________                                    

Example 13

A 75 gallon glass lined reactor was charged with 174.1 lb. of water and75 lb. of TTA. After sealing the reactor, 50.4 lb. of a 12.5% sodiumhypochlorite solution (this represents 15% of the total charge of 335.8lb.) was transferred to the reactor. The reaction mixture was heated to45° C., and after the temperature was stable the remaining sodiumhypochlorite solution was added over a period of 2 hours whilemaintaining the temperature at 47°-50° C. The two step addition ofsodium hypochlorite was done due to the design characteristics of themixer being employed. After the sodium hypochlorite feed was complete,the temperature was held at 50° C. for 1 hour. The product was analyzedby LC-UV area percent and ¹³ C NMR. The composition of the product wasas follows: 8.5% residual TTA, 80.3% Cl-TTA, 10.8% di-Cl-TTA, <0.01%residual chlorine, pH 11.5.

Example 14

A sodium hypobromite solution was generated by mixing sodium bromide(21.4 g, 0.208 mol) dissolved in 50 g of water with sodium hypochlorite(100.5 g, 12.2% solution, 0.165 mol) prior to use. The sodiumhypobromite solution was added to a stirred slurry of TTA (20.0 g, 0.15mol) in 76.5 g of water over a period of 2 hours. The temperature wasmaintained at 30°-35° C. The equipment was covered with aluminum foil toprotect it from light. After the sodium hypobromite addition wascomplete, the reaction mixture was held at 35°-40° F. for 4 hours. Theproduct was analyzed by LC-UV area percent and ¹³ C NMR. The compositionof the product was as follows: 6.1% residual TTA, 81.5% Br-TTA, 12.1%di-Br-TTA, pH 9.9.

Comparative Example 15

TTA (30 g, 0.225 mol) was dissolved in aqueous acetic acid (60 mL, 1:1ratio) by heating to 32° C. The solution was cooled with an ice bath andheld below 20° C. during the addition of sodium hypochlorite solution(366 g, 5.25% sodium hypochlorite, 0.259 mol). After the addition, thereaction mixture was allowed to reach room temperature and was stirredfor 24 hours. During this time a sticky material separated. The aqueouslayer was decanted and the sticky yellow material was dissolved inmethylene chloride (300 mL). A flock formed and was filtered off (solid1, 13.9 g). The methylene chloride was removed to obtain a waxy yellowsolid (solid 2, 27.5 g). NMR analysis showed an apparent separation ofisomers between the two solids. This was confirmed by LC/MS analysis.The composition of the solids was as follows:

    Solid 1: 18.7% TTA, 70.5% Cl-TTA, 10.0% di-Cl-TTA

    Solid 2: 0% TTA, 76.9% Cl-TTA, 7.2% di-Cl-TTA

The above examples show that the halo-benzotriazoles of the presentinvention are effective corrosion inhibitors even in the presence ofchlorine.

While the present invention has been described with respect toparticular embodiments thereof, it is apparent that numerous other formsand modifications of this invention will be obvious to those skilled inthe art. The appended claims and this invention generally should beconstrued to cover all such obvious forms and modifications which arewithin the true spirit and scope of the present invention.

What is claimed is:
 1. A process for preparing halo-benzotriazole comprising mixing an aqueous solution of sodium hypohalite with an aqueous slurry of a benzotriazole and maintaining the mixture at a temperature of from about 30° to about 50° C. for a period of time sufficient to form said halo-benzotriazole solution.
 2. The process of claim 1 wherein the molar ratio of sodium hypohalite to benzotriazole is about 1:1.
 3. The process of claim 1 wherein said sodium hypohalite is selected from the group consisting of sodium hypochlorite and sodium hypobromite.
 4. The process of claim 1 wherein said halo-benzotriazole is chloro-tolyltriazole.
 5. The process of claim 1 wherein said halo-benzotriazole is chlorobenzotriazole.
 6. The process of claim 1 wherein said halo-benzotriazole is bromo-tolyltriazole.
 7. The process of claim 1 wherein said mixture is maintained at a pH of from about 8.7 to
 12. 8. An aqueous halo-tolyltriazole solution formed by mixing an aqueous solution of sodium hypohalite with an aqueous slurry of tolyltriazole and maintaining the mixture at a temperature of from about 30°to about 50° C. for a period of time sufficient to form said aqueous halo-tolyltriazole solution.
 9. The aqueous halo-tolyltriazole solution of claim 8 wherein the molar ratio of sodium hypohalite to tolyltriazole is about 1:1.
 10. The aqueous halo-tolyltriazole solution of claim 8 wherein said sodium hypohalite is selected from the group consisting of sodium hypochlorite and sodium hypobromite.
 11. The aqueous halo-tolyltriazole solution of claim 8 wherein said halo-tolyltriazole is chlorotolyltriazole.
 12. The aqueous halo-tolyltriazole solution of claim 8 wherein said halo-tolyltriazole is bromotolyltriazole.
 13. The aqueous halo-tolyltriazole solution of claim 8 wherein said mixture is maintained at a pH of from about 8.7 to
 12. 